In semiconductor manufacturing, the formation of micro-electromechanical systems (MEMS) on semiconductor wafers uses tools and techniques that have been previously developed for the Integrated Circuit (IC) industry to build microscopic machines. These MEMS devices can be built at the same time across the surface of the wafer, thereby requiring little to no assembly.
Bulk micromachining is a fabrication technique which builds mechanical elements by starting with a silicon wafer, and then etching away unwanted parts, and being left with useful mechanical devices. MEMS devices are often formed utilizing bulk micromachining, wherein lithographic processes are utilized in MEMS fabrication. In such bulk micromachining, the silicon wafer is patterned and subsequently submersed into a liquid etchant in order to dissolve any exposed silicon. The remaining silicon or other material generally forms the MEMS device.
Various pressure sensors, position sensors, and acceleration sensors, for example, are commonly formed using MEMS fabrication techniques. Such MEMS devices offer numerous advantages over traditional sensors, as they are typically more cost efficient, reliable, relatively easy to manufacture, and there is often very good repeatability between devices.
One reliability problem commonly observed with MEMS devices, however, is stiction, or the adhesion of contacting surfaces due to surface forces. Generally, stiction is the static friction that needs to be overcome in order to enable relative motion of stationary objects that are in contact with one another. When two surfaces with areas below the micrometer range come into close proximity, such as evidenced in MEMS devices, they may adhere together, thus limiting the reliability of the MEMS device. At this scale, the two main failure factors of MEMS devices are electrostatic or charge-induced stiction, and/or Van der Waals force-induced stiction. Such stiction issues present various problems that have heretofore been difficult to address.